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BGP Fundamentals

Here you will find answers to BGP Fundamentals Questions

Question 1

Based on the topology diagram shown in the exhibit, when should BGP be used as the routing protocol between the customer and the ISP?

BGP.jpg

A. If physical link failures can not be detected by the link-level procedures.
B. If the customer wants to affect how the ISP will route the customer’s traffic out to the rest of the Internet.
C. If the ISP does not support static routing with the customer.
D. If the customer is using provider-assigned (PA) addresses inside the customer’s network.
E. If the customer is using private addresses inside the customer’s network.

 

Answer: A

Question 2

Based on the network diagram shown in the exhibit, what is the correct configuration on the customer edge router used to conditionally announce the customer networks to the ISP?

BGP_customer_edge_router.jpg

A. router bgp 65001
! neighbor commands not shown
network 192.168.8.0 mask 255.255.252.0
!
ip route 192.168.8.0 255.255.252.0 192.168.8.33

B. router bgp 65001
! neighbor commands not shown
aggregate-address 192.168.8.0 255.255.252.0 summary-only
!
ip route 192.168.8.0 255.255.252.0 192.168.8.33

C. router bgp 65001
! neighbor commands not shown
network 192.168.8.0
network 192.168.9.0
network 192.168.10.0
network 192.168.11.0
!
ip route 192.168.8.0 255.255.255.0 null0
ip route 192.168.9.0 255.255.255.0 null0
ip route 192.168.10.0 255.255.255.0 null0
ip route 192.168.11.0 255.255.255.0 null0

D. router bgp 65001
! neighbor commands not shown
aggregate-address 192.168.8.0 255.255.252.0 summary-only
!
router ospf 1
network 192.168.8.0 0.0.3.255 area 0

E. router bgp 65001
! neighbor commands not shown
aggregate-address 192.168.8.0 255.255.252.0
!
ip route 192.168.8.0 255.255.252.0 null0

 

Answer: A

Question 3

Which two statements about a transit AS are correct? (Choose two)

A. A transit AS has eBGP connection(s) to only one external AS.
B. Routes between ASs are always exchanged via eBGP.
C. A transit AS uses an IGP like OSPF or ISIS to propagate the external networks within the transit AS.
D. Core routers within a transit AS normally use default routing to reach the external networks.
E. iBGP sessions can be established between non directly connected routers.

 

Answer: B E

Question 4

Which command is used to configure the external, confederation-wide AS number?

A. router(config)#router bgp {as-number}
B. router(config-router)#bgp confederation peers {as-number}
C. router(config-router)#bgp confederation identifier {as-number}
D. router(config-router)#bgp cluster-id {as-number}
E. router(config-router)#neighbor {ip address} remote-as {as-number}

Answer: C

Question 5

In a Transit AS, how do the internal routers within the Transit AS forward packets destined for the external networks using a scalable solution?

A. using the default route
B. using the IGP routes where the external networks are redistributed into the IGP by the edge routers 
C. using the EBGP routes where the external networks are redistributed into the IBGP by the edge routers 
D. using the IBGP routes, then using recursive lookup based on IGP information to resolve the BGP next-hop

 

Answer: D

Question 6

Given the following configurations, R2 and R3 are not able to successfully establish the iBGP session using the loopback 0 interfaces. What could be the cause of this problem?

iBGP_session.jpg

hostname R2
!
interface loopback 0
ip address 2.2.2.2
!
interface e0
ip address 10.1.1.1 255.255.255.0
no shut
!
interface e1
ip address 10.2.2.1 255.255.255.0
no shut
!
router bgp 65101
neighbor 172.16.1.1 remote-as 65100
neighbor 3.3.3.3 remote-as 65101
!
router eigrp 101
network 10.0.0.0
network 2.0.0.0
!
!
output omitted
!

hostname R3
!
interface loopback 0
ip address 3.3.3.3
!
interface e0
ip address 10.1.1.2 255.255.255.0
no shut
!
interface e1
ip address 10.2.2.2 255.255.255.0
no shut
!
router bgp 65101
neighbor 192.168.1.1 remote-as 65102
neighbor 2.2.2.2 remote-as 65101
!
router eigrp 101
network 10.0.0.0
network 3.0.0.0
!
A. The “No Sync” BGP configuration command is missing.
B. R2 and R3 are not using the loopback0 IP address as the source address for the BGP messages to each other.
C. The “network 2.0.0.0” BGP configuration command is missing on R2 and the “network 3.0.0.0” BGP configuration command is missing on R3.
D. The “neighbor 2.2.2.2 ibgp-multihop 2” BGP configuration command is missing on R3 and the “neighbor 3.3.3.3 ibgp-multihop 2” BGP configuration command is missing on R2.

 

Answer: B

Question 7

What are two purposes of the BGP scan-time command? (Choose two)

A. to tune the BGP process which walks the BGP table and confirms the reachability of next hops
B. to allow faster detection of downed BGP peers
C. to improve BGP convergence time
D. to tune the BGP update interval
E. to decrease the effects of unstable routes by increasing the route suppression time

 

Answer: A C

Question 8

If there is no exact match in the local routing table, what three conditions would result in BGP introducing the classful network 172.0.0.0 with the mask 255.0.0.0 into the BGP table? (Choose three)

A. no auto-summary is configured under the router bgp {as no.} command
B. network 172.0.0.0 is configured under the router bgp {as no.} command
C. any classful network must exist in the BGP table
D. auto-summary is enabled under the router bgp {as no.} command
E. the routing table contains the subnet 172.172.172.0 with a subnet mask of 255.255.255.0
F. a classless network must exist in the BGP table

 

Answer: B D E

Categories: BGP + MPLS 642-691 Exam Tags:
  1. SC
    April 16th, 2011 at 15:23 | #1

    Dear iptut
    I think that the answers on Q.2 are duplicate by mistake…

  2. iptut
    April 17th, 2011 at 00:16 | #2

    Thanks for your detection. I updated it!

  3. Anonymous
    April 21st, 2011 at 02:50 | #3

    Question number 2 question is confusing as it doesn’t have details. I need to understand the following.
    1) Where is the ip address 192.168.8.33 assigned?
    2) What does the static route p route 192.168.8.0 255.255.252.0 192.168.8.33 accomplish?

  4. Ranjeet Badhe
    April 21st, 2011 at 02:51 | #4

    Question number 2 question is confusing as it doesn’t have details. I need to understand the following.
    1) Where is the ip address 192.168.8.33 assigned?
    2) What does the static route p route 192.168.8.0 255.255.252.0 192.168.8.33 accomplish?

  5. GK
    April 28th, 2011 at 15:46 | #5

    Hi everybody…

    I’m planning to take CCIP BGP exam, please can any one share the BGP PDF… to study..

  6. Ranjeet Badhe
    May 6th, 2011 at 07:19 | #6

    GK , share your contact details so that I can suggest you on CCIP BGP 642-661 preparation and share some documents.

  7. warmachine
    May 20th, 2011 at 10:28 | #7

    hi, anybody has a bgp cbt nuggets?

  8. warmachine
    June 1st, 2011 at 12:37 | #8

    you need the ine BGP + MPLS video ‘s they rock your world!

  9. CCIP
    June 9th, 2011 at 14:18 | #9

    @warmachine pls kind share the link for BGP + MPLS……….

  10. CCIP
    June 9th, 2011 at 14:19 | #10

    @warmachine link MPLS+BGP videos

  11. Kadeesa
    July 16th, 2011 at 04:01 | #11

    Can anyone explain Q1 for me? I cannot get it !!! 🙁

  12. Jason
    September 13th, 2011 at 07:33 | #12

    I;m stuck at a question on BGP. Can anyone point me to a good source to review or have a simple lab that can demonstrate this ?

    The question is asking:

    Refer to the exhibit. Based upon the configuration, you need to understand why the policy routing match counts are not increasing.

    R1#show route-map divert
    route-map divert, permit, sequence 1
    Match clauses:
    ip address (access-lists): 101
    Set clauses:
    ip next-hop 212.50.185.126
    ip next-hop recursive 192.0.0.1
    ip default next-hop 212.50.185.125
    Policy routing matches: 0 packets, 0 bytes

    a) check the routing table for 212.50.185.126
    b) check the access list for log hits
    c) remove any two of the set clauses (multiple set clause entries will cause PBR to use the routing table)
    d) confirm if there are other problematic route-map statements that precede divert

    What is the correct ans to this question and why ?

  13. Emmanuel
    October 11th, 2011 at 21:07 | #13

    Hi Jason,
    Answer is B, if the ACL hit count is not increasing, it means no interesting packet is being matched. So, PBR will have nothing to route

  14. Anonymous
    March 28th, 2012 at 11:35 | #14

    passed ccnp ccip

  15. MB
    April 7th, 2012 at 10:51 | #15

    Can Anyone please explain Question 8???

  16. mkioga
    April 12th, 2012 at 14:19 | #16

    For Question 8, I think if we don’t have an exact match in local routing table ( match 172.0.0.0/8) then we need all three conditions for the classful network 172.0.0.0/8 to be in BGP table.

    router bgp AS_#
    network 172.0.0.0
    auto-summary

    And the routing table needs to contains a subnet (e.g. 172.172.172.0/24) that is under the main classful network 172.0.0.0/8

    Then there will be a BGP route with the classful network (172.0.0.0/8) being advertised

    If auto-summary is disabled however, just having a subnet (172.172.172.0/24) of this major network (172.0.0.0/8) in the IP routing table is not sufficient to inject this major network (172.0.0.0/8) in the BGP table. We would have to have an exact match to this network (172.0.0.0/8) in our IP routing table for the major network (172.0.0.0/8) to be inserted in BGP table.

  17. Attal
    April 18th, 2012 at 22:03 | #17

    I think question 8 is wrong, the network statement should be at least (network 172.172.0.0) for it to work and since autosuummary is enabled and 172.172.172.0/24 is in routing table a summary route will be generated.
    if we were to use 172.0.0.0 with autosummary the bgp process will look for 172.0.0.0/16.

  18. cciphopeful
    April 20th, 2012 at 12:37 | #18

    does anyone has the latest CBT nuggets 642-661 by Jeremy Ciaora?

  19. Anonymous
    April 26th, 2012 at 04:12 | #19

    @Attal Its correct.

    > 172.0.0.0 with autosummary the bgp process will look for 172.0.0.0/16.

    Ur mistaking it with private addresses (172.16.0.0/16). Class B addresss start from
    128.0.0.0 to 191.255.255.255 and use a /8 mask.

  20. Peter
    May 12th, 2012 at 00:24 | #20

    @Anonymous, Class B address use a /16 mask.
    @Attal, you are absolutely correct.

  21. CCIPsoon
    May 23rd, 2012 at 10:27 | #21

    does anybody know if DoDo 80q still valid for MPLS+BGP exam?

  22. xxox
    July 15th, 2012 at 17:02 | #22

    somone know why the answer for Q.1 is A?

  23. CCIP ASAP
    July 22nd, 2012 at 19:07 | #23

    i just pass MPLS+bgp today dodo 80 q is enough thanks great forum pass 980

  24. zeroboretv
    July 25th, 2012 at 18:31 | #24

    There is another version of #6. Where the “network 2.0.0.0” and “network 3.0.0.0” statements are missing, and instead the “neighbor 3.3.3.3 update-source loopback0” and “neighbor 2.2.2.2 update-source loopback0” ARE present. In which case the answer = C. The “network 2.0.0.0″ BGP configuration command is missing on R2 and the “network 3.0.0.0″ BGP configuration command is missing on R3.

  25. Auth
    August 30th, 2012 at 08:17 | #25

    == left router ==router bgp 200 nebgoihr 1.1.1.1 remote-as 100 nebgoihr 1.1.1.1 ebgp-multihop 2 nebgoihr 1.1.1.1 update-source Loopback0!ip route 1.1.1.1 255.255.255.255 192.196.12.1== right router ==router bgp 100 nebgoihr 2.2.2.2 remote-as 200 nebgoihr 2.2.2.2 ebgp-multihop 2 nebgoihr 2.2.2.2 update-source Loopback0!ip route 2.2.2.2 255.255.255.255 192.168.12.2

  26. Dinesh Kumar
    December 7th, 2012 at 02:13 | #26

    in CCNA there is tutorial available for each topic before taking the questions and answers. but here it was not available if its available better for us to recalling… Since CCNA explanation given was very simple to learn by anyone.. same expecting for each topic in CCNP as well as CCI………..

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